This avoids failing builds with:
NameError: name 'html_theme' is not defined
It also makes the theme configuration explicit and correctly set up.
Signed-off-by: Andrei Gherzan <andrei@gherzan.com>
myst_parser is not in the default Read The Docs container by default.
Pull it in as we use it for parsing the markdown files.
Signed-off-by: Andrei Gherzan <andrei@gherzan.com>